1. Field of the Invention
This invention relates to an expansion valve for use in an air conditioner of a car, refrigerating display case, or the like.
2. Description of the Prior Art
FIG. 5 shows a cooling cycle of an air conditioner. The cooling cycle 50 comprises a compressor 51 driven by a motor or its equivalent, a condenser 52 for cooling and condensing a gaseous refrigerant heated and pressurized by the compressor 51, a liquid tank 53 for separating the refrigerant condensed by the condenser 52 into vapor and liquid and for removing moisture and dust from the refrigerant, an expansion valve 54 for expanding the refrigerant from the liquid tank 53, and an evaporator 55 for heat exchange between air and the refrigerant to cool the air to be blown into the compartment, which all are connected by a pipe network.
A general aspect of a conventional expansion valve, 54, used in the refrigeration cycle is shown in the cross-sectional view of FIG. 6, and its valve chamber is shown in FIG. 7 in an enlarged scale.
In FIG. 6, the expansion valve comprises a valve portion A for decreasing the pressure of a highly pressurized liquid refrigerant, and a power element portion B for controlling the opening rate of the valve portion A.
The power element portion B includes a power element outer shell 3 comprising an upper cover portion 1 and a lower support portion 2 (diaphragm receiver), and a diaphragm 4 sandwiched and welded between outer circumferential edges of the upper cover portion 1 and the lower support portion 2. The diaphragm 4 divides an interior space in the power element outer shell 3 into upper and lower chambers, namely, a pressurizing chamber 5 and an equalizing chamber 6, and the pressurizing chamber 5 communicates with the interior of a heat-sensitive cylinder 8 through a conduit 7.
The heat-sensitive cylinder 8 is provided at an exit portion of an evaporator (not shown) to detect the temperature of the refrigerant near the exit of the evaporator and to convert the temperature into a pressure which is the pressure of the power element space (pressurizing chamber 5). The pressure, when increased, gives a force for pressing the diaphragm 4 downwardly and for moving the valve member 9 in its opening direction.
The valve portion A comprises a valve body 10 in form of an outer shell made of brass and having an inlet 11 for introducing pressurized refrigerant and an outlet 12 for delivering depressurized refrigerant. The valve body 10 defines a valve chamber 13, and an equalizing path 14 communicating the valve chamber 13 with the equalizing chamber 6.
The valve body 10 includes a hitching member 15 which is fixed to its lower threaded end by screw engagement. Assembled to and in the valve body 10 are a movement regulating member 16 which cooperates with the diaphragm 4 to regulate downward movements of the diaphragm 4; actuating rods 17 for transmitting the displacement of the diaphragm 4 to the lower mechanism (although only one actuating rod is illustrated, three rods are provided at predetermined intervals in the circumferential direction of a valve mover 18 to move vertically in three vertical holes formed in the valve body 10); a valve member 9 brought into contact with or away from a valve seat 19 (the drawing illustrates a needle valve supported on the valve mover 18); a biasing spring 20 which energizes the valve member 9 upwardly (toward the valve seat 19); and an adjusting member 21 for adjusting the biasing force of the spring 20.
The adjusting member 21 is a polygonal nut, e.g. a hexagonal nut, which is slidably received in the inner polygonal hole of the hitching member 15 and engages with an adjusting bolt 22 by screw engagement to move up and down in response to a rotation of the adjusting bolt 22. The adjusting bolt 22 has a polygonal lower end 22a to be rotated for adjustment, and rotatably received in the hitching member 15 through the seal of an O-ring 23 such that the lower end 22a projects downwardly from the lower end of the hitching member 15.
The hitching member 15 has a threaded open end with which a protective cap 25 having a seal packing 24 on its inner circumferential surface is removably attached such that an operator can rotate the adjusting bolt 22 by removing the protective cap 25.
FIG. 4 is a fragmentary view of an orifice portion shown in FIG. 7. The orifice, 150, formed in the valve body 10 has one end behaving as the valve seat 19. The valve body 9 moved to and away from the valve seat 19 provides a flow path 160.
In case of an expansion valve in which the orifice 150 has a small inner diameter D1 across the inner wall 152 and is relatively long and in which refrigerant flows in the direction shown by the arrow F, the refrigerant running through the orifice 150 suddenly expands in the flow path 160 between the orifice 150 and the valve body 9.
Eventually, the temperature of the refrigerant decreases, for example, from 40.degree. C. higher than the room temperature within the orifice 150 to -20.degree. C. after expansion.
In this process, moisture contained in the refrigerant is likely to cohere into water drops on surfaces of the valve member 9 and the valve seat 19 and often bars the flow path.